2017 Build Log - Jet Chopper 30 Hull

[oscarel]

Worked on the hatch a bit last few days, I epoxied 1/8" aluminum flat stock under the 4 corners then drilled and tapped them for Stainless M3 screws. I bought these nifty flat o-rings and those should seal nicely. Still wondering if I can find some thin membrane to line the hatch opening with. I will be using hatch tape, but would add like to add something between the hatch and hull as ProBoat does.

[ATTACH=CONFIG]150636[/ATTACH]

[ATTACH=CONFIG]150637[/ATTACH]

[ATTACH=CONFIG]150638[/ATTACH]

[ATTACH=CONFIG]150639[/ATTACH]

Where did you get the foam? I have some from Dennis love on jrcbd and it works very well.

Sent from my SM-G930T using Tapatalk

[Tamelesstgr]

Yes, I got that foam from Dennis Love, from the Elite RC Boat group on Facebook.

[oscarel]

Cool, I have not tried it in a heavier electric yet. Gas boats so far it works great.

[Tamelesstgr]

Made the maiden run today on the JetChopper 30. Leak test went well so we buttoned her up and sent her off. A quick test to make sure the cooling lines were flowing and my son stabbed the throttle. We started out with a Graupner 442 2-blade. I have the COG set at 33% (10" from transom) and she for sure running wet.

Datalogger showed:
Max Amps: 77.23
Max Watts: 1143
Max RPM: 28,571
Average Loaded RPM: 26,500 (Seems a little low, might come up with not plowing water?)
GPS Speed: 30.2mph
Max ESC Temp: 87.2
Max Motor Temp: 68.4


This is an SSS 3674 - 2075kv 4-pole motor on 4s
Stinger and trim tabs all set to neutral

I think setting the COG back to 30% at 9" should be my next step.

I also noted that while the motor and esc were cool, the water is very cold in my pond, and the water flow coming from the rudder pickup was not to my liking so I will add the second pickup.

I also have a slight alignment problem as I can hear the flex hitting the stuffing tube. I'm going to swap in another motor coupler to see if that helps at all, if not I might need to adjust the set screws on the motor mount.

JC30 2075KV 4S G442 Prop 3-31-17 Gauges.JPG

JC30 2075KV 4S G442 Prop 3-31-17 Temp Chart.jpg

JC30 2075KV 4S G442 Prop 3-31-17 Amps Chart.jpg

JC30 2075KV 4S G442 Prop 3-31-17 RPM Chart.jpg

[martin]

A friend of mine built a Jetchopper 30 with a Leopard 3674 2200kv on 4s, I only saw it run a few times. But it did run very wet with its bow down, he had no trim tabs on the hull so not that causing the problem. I don't know where he had the cg set but worth checking if theirs any hook in the hull.

[Tamelesstgr]

The hull does have quite a bit of hook in it, noticed it as soon as I received the hull.

[martin]

Although quite rare their are some hulls with built in hook, the Seaducer monos for one. Seaducer tell you that this hook is built in on purpose & not to take the hook out. But not sure on the Jetchopper hulls whether any hook is just a distortion in the hull that should not be their. I would email the guy that makes them & ask if the hook should be their rather than just filling the hook out first.

[martin]

On the Jetchopper 30 website are the build & set up instructions, it states. The hook near the transom shall be grinded off to make a near perfect straight line, try moving your cg back first though. If that dosnt improve things I would look at filling the hook in the hull.

[785boats]

Mine has a hook in it also. As did the first one I built up years ago. I filled the hooks in the first one. it was a much better boat then.

Kenny, as suggested above, move the cog back & raise your trim tabs up to well above level to make sure they are not pushing the nose down too. Maybe put a slight positive angle in the strut too, if it is still running wet. If all that fails then as Martin suggests, you will need to fill the hooks.

[Tamelesstgr]

Will try those suggestions. What would I use if I end up deciding to fill the bottom?

[martin]

Will try those suggestions. What would I use if I end up deciding to fill the bottom?

I use car body filler, its quick drying in around 15 minuets so you can use put multiple layers if need be. Easy to sand & cheap from auto stores, just paint after.

[fweasel]

Just for rookie clarification, a "hook" is an imperfection in the bottom of the hull? I'm envisioning it as a depression followed by a ridge just before the transom.

[Tamelesstgr]

Yes, it's basically that the bottom of the hull is not flat, I'll take some pictures later.

[martin]

Yes a hook is a distortion in the hull bottom where the distortion is concaved, this sucks the hull down to the water. You can also get a rocker distortion in the hull which is which is the opposite to a concave, which causes the hull to porpoise.

[martin]

Hooks & rockers also apply to both monos & cat hull running surfaces.